Optical medical imaging modalities such as Time-Domain and Continuous Wave show great promise as techniques for imaging breast tissue, as well as the brain and other body parts. In TD, the objective is to analyze the temporal point spread function (TPSF) of an injected pulse of light as it is diffused in the tissue. With CW, the attenuation of a continuous light source is measured. The information extracted from the TPSF and the attenuation signal is used in constructing medically useful images.
For example, one can extract time-gated attenuation information from the TPSF which provides high quality images albeit of lower resolution than other modalities such as X-ray imaging. Thus, it is unclear whether the spatial resolution provided by optical imaging is adeuate for diagnosing breast cancer based on morphology.
CW and TPSF data, when processed adequately, can be used to extract absorption values from raw measurements. For example, the TPSF can be used to decouple the light attenuation into absorption and scattering components. This extra information may be clinically useful. Moreover, one can obtain the tissue absorption spectrum by performing time-domain measurements at multiple wavelengths. In tissue there are several molecules which absorb the light and are known as chromophores. Spectroscopic analysis of the tissue absorption spectrum permits chromophore concentrations to be measured. Furthermore, combination of the chromophore concentrations can yield physiological information, as opposed to morphologic information, which could provide a more medically useful image.
The problem is one of knowing which are the dominant chromophores to include in a tissue model and then choosing the “best” wavelengths to deduce their concentrations most accurately.